Plastics and metals have been conventionally employed as materials for internal parts of automobiles or electronics devices. Although use applications of the plastics to electronics devices, general merchandises, and automobile parts or the like have been expanded because the plastics are lighter than the metals and the like, lighter materials having excellent properties such as strength and shock resistance are required in terms of energy saving or the like. One of such materials is a resin expanded molded body.
A resin expanded molded body obtained by foaming a blend resin of a polystyrene resin and a polyphenylene ether resin has been known as an example (Patent Literatures 1 and 2). Flame-retardant expandable beads to which flame retardancy is given by adding a flame retardant have been known (Patent Literatures 3 and 4).